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Rick, HVAC Supervisor

Category: HVAC

Satisfied Customers: 19541

Experience: 40+ yrs. experience as a licensed oil & gas technician.

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I have a weil mclain oil fired hotwater boiler with 2 zones.

Customer Question

I have a weil mclain oil fired hotwater boiler with 2 zones. the upstairs zone will not shut off even with the thermostat down I switched thermostats witch are new with no result. any suggestions? my name is*****

Ok, is the pump for the upstairs running? If you can't tell put a screwdriver handle to your ear and the tip on the pump. If it's running you should be able to hear it spinning. I also need the relay brand and model that controls that pump if it's running.

Ok, is it running now with a thermostat that's turned off? if so then disconnect the thermostat leads (T & T / R & W) on the relay and see if the pump shuts off. If it's not running now then do this when the pump runs when it shouldn't. If the pump stops when you disconnect the leads at the relay then reconnect the leads and go to the thermostat and disconnect the leads on R & W. If the pump continues to run you have a live short in the thermostat wiring between the relay and the stat. If the pump shuts off when you disconnect the thermostat then the thermostat is faulty.

OK, the only other cause for heat in a zone when it's not calling aside from a bad relay (pump runs after you disconnect T & T at the relay) is a flow check that's leaking by. A flow check is a type of check valve specific to hot water heating systems that stops gravity water circulation to a zone when the pump isn't running. See attached pics for typical types